Staging and Grading Systems for Childhood Soft Tissue Sarcoma
Table 6. Anatomic Stage/Prognostic Groupsa continued...
In most cases, accurate histopathologic classification of STSs alone does not yield optimal information about their clinical behavior. Therefore, several histologic parameters, including degree of cellularity, cellular pleomorphism, mitotic activity, degree of necrosis, and invasive growth, are evaluated in the grading process. This process is used to improve the correlation between histologic findings and clinical outcome. In children, grading of STSs is compromised by the good prognosis of certain tumors, such as infantile fibrosarcoma and hemangiopericytoma, which have a good prognosis in children younger than 4 years, and also angiomatoid fibrous histiocytoma and dermatosarcoma protuberans, which may recur locally if incompletely excised, but usually do not metastasize.
Testing a grading system within the pediatric population is difficult because of the rarity of these neoplasms. In March 1986, the Pediatric Oncology Group (POG) conducted a prospective study on pediatric STSs other than rhabdomyosarcoma and devised the grading system that is shown below. Analysis of outcome for patients with localized STSs other than rhabdomyosarcoma demonstrated that patients with grade 3 tumors fared significantly worse than those with grade 1 or grade 2 lesions. This finding suggests that this system can accurately predict the clinical behavior of nonrhabdomyosarcomatous STS.[5,6,7]
The grading systems developed by the POG and the French Federation of Comprehensive Cancer Centers (Fédération Nationale des Centres de Lutte Contre Le Cancer [FNCLCC]) Sarcoma Group are described below. These grading systems are being compared by the central review pathologists on the COG-ARST0332 study. The study has closed and results are pending.
POG grading system
The POG grading system is described below:
Grade I lesions are based on histologic type, well-differentiated cytohistologic features, and/or age of the patient.
- Liposarcoma–myxoid or well-differentiated.
- Well-differentiated or infantile (aged ≤4 years) fibrosarcoma.
- Well-differentiated or infantile (aged ≤4 years) hemangiopericytoma.
- Well-differentiated malignant peripheral nerve sheath tumor.
- Angiomatoid fibrous histiocytoma.
- Dermatofibrosarcoma protuberans.
- Myxoid chondrosarcoma.
Grade II lesions are STSs not included in grade I or III by histologic diagnosis (with <5 mitoses/10 high-power fields or <15% necrosis):
- 15% or less of the surface area shows necrosis (primary criteria).
- The mitotic count is <5 mitotic figures per 10 high-power fields (40X objective) (primary criteria).
- Nuclear atypia is not marked (secondary criteria).
- The tumor is not markedly cellular (secondary criteria).